There are a number of firearm suppressors known in the art. Firearm suppressors generally are utilized to suppress the sound that occurs when a projectile is fired through the firearm to which the suppressor is attached. Integral suppressors are one type known in the art. Generally in an integral suppressor baffles are machined into or attached to an existing barrel. A suppressor sleeve will cover the baffles and in some cases all or part of the barrel. Integral suppressors generally include a port in the section of the barrel that is covered by the suppressor sleeve. The vent or port allows gas to vent in an annular chamber created by the suppressor sleeve and a section of the barrel while the projectile is in the barrel. The venting of the gas at this stage decreases the muzzle velocity of the projectile and reduces the sound level or decibel level of the shot.
Depending upon the type of ammunition used, a vent may or may not be desirable. For example, subsonic ammunition may lose additional velocity and impact force if shot through a suppressor with an open vent. For this reason, subsonic ammo is preferably shot in a barrel without a vent to maintain maximum velocity. Bulk ammunition and high velocity rounds can have velocity slowed to subsonic when used with an integral suppressor with an appropriately sized open vent. At times, however, it may be desirable to suppress sound but to not lose velocity and to maintain impact force even with standard and high velocity rounds, but especially with low velocity subsonic rounds where the additional loss of velocity is greatly increased by having an unrestricted port that allows excess gas to escape from the barrel into the suppressor.